There are several ways to start a review of our dietary choices – some more analytical, others more subjective. I personally enjoy numbers. And although there is more to a healthy diet than calories in calories out, I believe it is helpful to start looking at some numbers and be aware of what could be your body needs. I say could be, because there is always an associated error with this type of calculation, so don’t focus too much on the number itself.
Base Metabolic Rate
The first step we need to take before figuring out our caloric needs is to calculate the Base Metabolic Rate. In a simple way this is the minimum amount of calories our body needs to function, not taking into consideration our daily activities (there will be an additional factor for that in the second step.
There are lab tests to do this more accurately, but using the existent formulas are usually enough to have some direction. Here you can check two of them: the Revised Harris-Benedict Equation, a reviewed version of the original formula from 1919 made by Roza and Shizgal in 1984 and the more recent Mifflin St. Jeor, that is usually considered more accurate.
Both take into account the person weight, height and age. There is also an adjustment by gender in each.
Mifflin St. Jeor Equation
Male: 10 x [weight in kg] + 6.25 x [height in cm] – 5 x [age] + 5
Female: 10 x [weight in kg] + 6.25 x [height in cm] – 5 x [age] – 161
Revised Harris-Benedict Equation
Male: 13.397 x [weight in kg] + 4.799 x [height in cm] – 5.677 x [age] + 88.362
Female: 9.247 x [weight in kg] + 3.098 x [height in cm] – 4.330 x [age] + 447.593
For example, a 27 years old female with 160cm and 60 kg would get 1304 from the Mifflin St. Jeor equation and 1381 from the Revised Harris-Benedict. I will use the first one as reference.
Total Daily Energy Expenditure
As indicated in the beginning, one thing is to calculate the energy your body needs to be “alive”, other is how much you really use during a normal day. In other to get that second number the BMR is usually multiplied by a factor that goes from 1.2 to 1.9 depending on the person activity level.
Check the table above and select the factor you believe better describes your current situation (of soon to be if you are starting a training plan). For example, if you are starting the Active Plan and have a sedentary job select between 1.375 and 1.55 depending on the number of days you will be able to train.
Going back to our example, if following the Active Plan, if our female with 27 year has a sedentary job, would be expending around 1800 kcal per day (using 1.375 as factor to account for possible missing days).
Calorie deficit or surplus
By now you should already have been able to calculate the amount of calories you need to maintain your weight. The following step depends on your goal. To lose weight you will have to reduce the amount of calories you eat. To gain muscle you will have to increase.
As a rule of thumb, to lose 1kg you would need a cumulative calorie deficit of 7000 kcal. That is 1000 kcal per day, which is a very extreme weight loss goal. A more attainable one would be 0,5kg per week, or around 500kcal per day. In our example would result in 1300 daily kcal. If we aimed for 1kg we would get less than 1200kcal, and that would be too low. 1200kcal is considered as the minimum for any adult.
As for gaining weight, while you need some surplus, it is actually less than what most people believe necessary. Usually 100 to 200 kcal is sufficient to give the body the right conditions to gain muscle, assuming you are giving it the right nutrients as well. Yes, if you eat more than that you will gain more weight – but probably not only the muscle mass you wanted, but also some fat as well. Since the process of losing fat sometimes also makes you lose some lean mass, it is better to avoid it when your goal is to gain muscle.
Calories are important. But more than calories we should always think about nutrients, as those are the ones that fuel our body.
Now that you know how many calories you need to consume you are in conditions to move into the next topic: how to calculate each nutrient amount.
Check the next recommended post: define protein amount.